A technique of adding a flame retardant to a synthetic resin emulsion to impart flame retardancy has conventionally been employed for the purpose of imparting flame retardancy to a backing agent of a carpet, an adhesive agent, a coating agent and the like. Halogenated compounds such as brominated compounds having high flame retardant effect, or a mixture of the halogenated compound and antimony oxide are generally adopted as a flame retardant. For example, nuclear bromine-substituted aromatic compounds such as a decabromodiphenyl ether and tetrabromobisphenol A are known as a brominated compound as a flame retardant.
The problem, however, is that these halogenated compounds cause gas harmful to a human body by thermal decomposition, or are harmful to natural environments. Thus, a process for flame-retarding a backing agent and the like without using the halogenated compounds is desired.
Inorganic flame retardants, for example, a polyphosphate salt such as ammonium polyphosphate are studied as a flame retardant in place of such halogen flame retardants (for example, Patent Reference 1 (JP-A-9-310283) and Patent Reference 2 (JP-A-2001-31824)).
However, the addition of polyphosphate salt flame retardants to a synthetic resin emulsion occasionally causes a protective layer of the synthetic resin emulsion to be broken by hydrolysis of polyphosphate salt and thickened with time. In order to avoid such a problem, generally, special dispersant and resin are previously used for para-encapsulating polyphosphate before adding polyphosphate salt to a synthetic resin emulsion or adding polyphosphate salt to a synthetic resin emulsion after encapsulating polyphosphate salt. Thus, the stability of polyphosphate salt can be improved; however, the emulsion to which polyphosphoric acid is added in this manner is occasionally restricted in formulation. By adopting such a technique, the problem of storage stability is not solved, and harmful components are diffused from the encapsulated resin with time. Further, flame retardant performance of a polyphosphate salt may happen to be lowered. In addition, encapsulation leads to a rise in manufacturing costs thereof.
Large amount of dispersants are generally used for stably dispersing polyphosphate salt flame retardants in a synthetic resin emulsion. A surfactant is generally used as a dispersant, and when a surfactant freely exists in the emulsion, a part of the surfactant is decomposed, which may cause a phenomenon such that a decomposed article thereof (such as a nonylphenyl ether) is released into the air with time. Such a phenomenon is called “a fogging phenomenon”, and most of the decomposed article released into the air is harmful to a human body and environments. Thus, it is desired that the fogging phenomenon be restrained as much as possible from occurring.    Patent Reference 1: JP-A-9-310283    Patent Reference 2: JP-A-2001-31824